U.S. Pat. Nos. 5,627,218, 5,747,548, 7,550,203, 7,816,008, 7,981,510, 7,931,968, 8,231,937, 8,696,960, 8,986,582, and 7,541,091 the teachings of each of which are incorporated herein by reference in their entirety, teach many techniques for manufacturing compartmentalized resin pellets. In one embodiment, there are at least two zones, or regions in the pellet, preferably a core and a sheath.
Titanium catalysts for bottle grade polyesters are well known. They are used to produce exceptionally good colorless clear containers, such as those required for bottled water. However, the significant catalytic effect of titanium also catalyzes the production of acetaldehyde when the polyester resin is extruded and injection molded into the preform. The high amounts of acetaldehyde have limited the use of titanium catalyzed polyesters in water bottles.
Phosphorus compounds for bottle grade polyesters are also well known. They are used to stabilize the polymer and prevent the formation of acetaldehyde. They are typically added to the polyester during the melt polycondensation phase. The ability to retard the formation of acetaldehyde has seen the use of phosphorus compounds grow in bottled water resins.
For example, U.S. Pat. No. 7,655,746, the teachings of which are incorporated herein by reference in their entirety, teaches adding a phosphorus compound (such as an ammonium salt of an oxyphosphorus acid compound containing an oxyphosphorus group) to a polyester composition during melt phase polymerization with a titanium polycondensation catalyst to reduce acetaldehyde. The phosphorus compound is added during melt phase polymerization after the polyester reaches an intrinsic viscosity (It.V.) of at least 0.45 dL/g. After melt phase polymerization the polyester has a final It.V of between 0.7 and 1.2 dL/g.
By adding the phosphorus compound during melt phase polymerization but prior to reaching the final It.V, the phosphorus compound deactivates the titanium polycondensation catalyst during the melt phase polymerization.
Because the titanium polycondensation catalyst is deactivated by the phosphorus compound during melt phase polymerization, the catalytic effect of the titanium compound is reduced or lost which leads to longer polymerization times.
U.S. Pat. No. 7,550,203, the teachings of which are incorporated herein by reference in their entirety, teaches controlling acetaldehyde in a polyester preform by placing an active oxidation catalyst in the core of a compartmentalized pellet to catalyze the reaction of acetaldehyde with oxygen after the preform is manufactured. U.S. Pat. No. 7,550,203 also teaches that certain phosphines act as a catalyst of acetaldehyde with oxygen.
It is desirable to be able to use titanium catalysts with phosphorus stabilizers providing benefits of both components to the bottle water industry. However, this has been historically impossible to the extent desired because the phosphorus compounds deactivate the titanium catalysts making it impossible for them to be used together in one resin pellet. Historically, the molar ratio of titanium to phosphorus had to be strictly controlled within a very narrow range to prevent the phosphorus from deactivating the titanium catalyst, which would have serious consequences for both the melt phase and solid state polymerization.
Non-limiting examples of phosphorus compounds which deactivate the titanium catalyst are those phosphorus compounds comprising phosphorus in an oxidation state higher than −1. There exists therefore, the need to create a polyester resin pellet or process to make a polyester resin pellet that can exploit the significant catalytic effect of titanium compounds and can also allow the injection molded preform from the resin to take advantage of the lower acetaldehyde provided by the phosphorus compounds.